Railway braking apparatus



2 Sheets-Sheet 1 5. o. GARRETT, JR. ETAL RAILWAY BRAKING APPARATUS Oct. 22, 1963 Filed March 17,- 1960 voct- 22,1963 E. o. GARRETT, JR..' ETAL $307,751

- RAILWAY BRAKING APPARATUS Filed March 17, 1960 2 Sheets-Sheet 2 n Q? Al I I. I g J I I I 19 b a m M 51 w 4a 19a I 65 I 29 6'1 3,107,751 RAILWAY BRAKING APPARATUS Edward 0. Garrett, Jr., Penn Hills Township, Allegheny County, and Glen V. Jefferson, Edgewood, Pa, assignors to Westinghouse Air Brake Company, Wilmerding, Pa., a corporation of Pennsylvania Filed Mar. 17, 1960, Ser. No. 15,712 3 Claims. (Cl. 188-62) Our invention relates to railway braking apparatus, and more particularly to inert car retarders, that is, car retarders in which brake beam are normally biased to a braking position by a resilient pressure for exerting retardation on cars in the retarder.

In gravity type classification yards, inert retarders may be advantageously used for various applications, such as, for example, to stop cars at a determined location on the storage tracks at the exit or lower end of the yard. Previously in classification yards, skate apparatus has been manually placed on the rail to engage the wheels of the first car moving down the storage track to stop the car reaching the desired location. The succeeding cars are then stopped when they come into contact with the first car. When the storage track is filled, an engine entering from the lower end of the yard couples to the cars to pull the cars out of the storage track. Before the cars can be pulled out the skate must be moved to release the skate and after the cars are pulled out the skate must be reset to its initial position. Workmen, so-called skatemen, must be employed to handle the skate apparatus.

. By using inert retarders instead of skate apparatus, the

need for skaternen is eliminated.

It is common practice in classification yards to provide a slight upgrade, about 0.3% in the last few hundred feet of storage tracks to assist in stopping the freely rolling cars. The inert retarders not only assist gravity in stopping the cars, but also prevent roll-back of easy rolling cars (for example those having roller bearing), which cars could otherwise be rolling back and hit the following on moving in the opposite direction.

Accordingly, it is a principal object of our invention to provide an improved inert car retarder in which the 'install, and which at the same time is highly efficient in operation.

In the attainment of the foregoing objects we provide a car retarder comprising two brake beams parallel to and straddling a track rail. Each of the beams is mounted on the upper end of vertically extending levers which are in turn pivotally mounted on brackets positioned adjacent the rails. The levers are mounted and operate as pairs. Brake shoes are affixed to the brake beams for engaging the wheels of railway cars, and a coil spring is mounted beneath the rail and extends between the lower end of the levers. A car wheel forces against the brake shoes and the upper end of the levers, whereby the levers pivot on their pins to compress the spring and thereby provide a clamping or braking action to the wheels. Means are provided for adjusting the force exerted against the wheels by said brake shoes.

Other objects and advantages of our invention will become apparent from the foregoing description in which like reference characters refer to like elements and in which:

FIG. 1 is a front elevational view in cross section of a retarder according to our invention;

, 3', l 07,751 Patented Oct. 22, 1963 FIG. 2 is a plan view of a portion of the retarder taken along the lines 22 of FIG. l'looking in the direction of the arrows;

FIG. 3 is a plan view showing two retarders positioned .on a track;

, FIG. 4 is an elevational view in cross section of a modification of the retarder of FIG. 1;

FIG. 4a is a fragmentary view taken along lines 4a-4a of FIG. 4 looking in the direction of the arrows;

FIG. 5 is an elevational view in cross section of a second modification of the retarderof FIG. 1; F FIG. 5a is an isometric view of a mounting bracket of IS. 5. I

Referring to FIGS. 1, 2 and 3, a pair of similar brake beams 11 and 13 each comprising an elongated inverted L-shaped flange, is positioned to straddle the running rail 14- on which the wheels 15 of cars which are to be retarded will pass. Rail 14 is mounted on the usual tie plate 43 which is in turn mounted on the cross ties 18. The brake beams 11 and 13 are each affixed as by bolts 29 and 16, respectively to the upper end of three pairs of vertical levers, one pair of levers 17 and 19 being shown in FIG. 1. The brake beams 11 and 13 are approximately 11 feet in overall length and have flared ends for purposes to be described hereinbelow. Brake shoeslla and 13a consisting of long narrow strips of wear resistant steel are welded to the upper edge, as oriented in FIG. 1, of each of brake beams 11 and 13, respectively, such that the braking force is effective at a relatively high point on the wheel which, as discussed below, provides an effective braking action. Each of levers 17 and 19 is pivotally supported on respective lugs 21 and 23, which lugs are mounted as by bolts 26 and 28 on respective L-shaped brackets 25 and 27 which brackets are'mounted on adjacent cross ties 18 as more fully described below. Lugs 21 and 23 are similar and each comprises a body portion and two spaced extending portions. Extending portions 21a and 21b on lug 21 are shown in FIG. '2; since the extending portions of lug 23 are similar to those of lug 21 they are not shown in FIG. 2.

Levers 17 and 19 each have apertured hubs 17a and 1901, respectively, formed intermediate their ends. Hub

17a fits between the two spaced portions 21a and 21b of lug 21 and hub 19a. fits between the two spaced portions of lug 23. Pivot or fulcrum pins 29 and 31 pass through the respective apertures in the extending portions of lugs 21 and 23, and through the apertured hubs 17a and 19a to permit pivoting of the levers 17 and 19 on their respective brackets. Pins 29 and 31 are heldin position by cotter pins, not numbered. As will be explained below, lugs 21 and 23 are adjustable with respect to brackets 25 and 27-to position respective pins 29 and 31 relative to center of wheels 15 on rail 14. The levers on a same side of rail 14 are located approximately 46" apart in the space between alternate ties and a lever 17 is positioned opposite each lever 19. p

The lower end of each of the levers 17 and 19 extends below the base of rail 14. A caging bolt 33 passes through apertures, not numbered, formed on the lower end of levers 17 and 19. The maximum spacing between the lower end of levers 17 and 19 is adjusted by bolt 33 and the associated lock nut 33a. A coil spring 35 is circumposed on bolt 33 between levers 17 and 19. The

end 35a of coil spring 35 are ground square i.e., flatis ing between brake shoes 11a and 13a. The normal mum thickness :of car wheels is about inches so the retarder will provide a braking action for even the thinnest wheels. A car wheel 15 entering the retarder will have a clamping or braking action applied thereto since said wheel will force against brake shoes 11a and 13ato tend to separate the upper end of the levers 17 and 19, consequently, pivoting levers 17 and 19 on pins 29 and 31 to cause the lower ends of the levers 17 and 19 to further compress spring 35 and thereby dissipate the energy of the moving car. The overall result is that the rctarder applies a braking force opposing car motion. Obviously, operation is bidirectional, that is, the retarder will apply a braking force to a car moving in either direction, and will also provide a braking force to a car standing in the retarder. However, the braking force is not so great as to prevent an engine from coupling to and pulling cars out of the retarder.

By initially controlling the spacing between the brake shoe 11a and 13a and by flaring the end of the retarders, entrance shock, that is, the shock produced when a wheel enters or leaves a retarder is minimized. To further minimize entrance shock, it is desirable that at the site where the retarders are located, the track gauge, that is, the distance between the two running rails be reduced by about A" to restrict lateral shifting of the car wheels.

Bolt 33 is essentially loose when a wheel is in the retarder; since nut 33a is a lock nut it remains as initially set to maintain the same maximum spacing between the lower ends of levers 17 and 19.

As noted above, to obtain the most eflective braking action the brake shoes 11a and 13a are affixed or formed on the top of brake beams 11 and 13 and the shoes are dimensioned to contact a relatively narrow area at a relatively high point on the wheel, as oriented in FIG. 1. It has been found that a braking force applied close to the periphery of the wheel is relatively ineffective and also tends to cause the wheels to climb out, i.e., push up and out of the retarder.

The length of spring 35 is selected such that with the braking apparatus adjusted to provide a five-inch spacing between brake shoes 11a and 13a, the spring 35 will be cocked, i.e., under some initial compression, with the length across the top of the spring 35 being less than the length across the bottom of the spring. This arrangement provides two important characteristics or advantages: First, the retarder is self-centering since the spring 35 tends to resume its least distorted position and will center itself on pivot pins 29 and 31 thus centering levers 17 and 19, beams 11 and 13 and brake shoes 11a and 13a; second, the lateral loading on the pivot pins 29 and 31 is always outwardly from the rail 14, that is, in the same direction as when a car wheel 15 enters into the retarder. Because the retarder is self-centering it tends to keep the wheels on the rails, i.e., in the event the wheels tends to climb out safe re-entrance of the wheel onto the rail is assured. Providing a lateral loading on the pins 29 and 31 in the same direction minimizes wear on the pins 29 and 31 by eliminating slapping movement of the pins within their apertures when a car enters or leaves the retarder which would be the case if the stress on the pins was initially inwardly toward the rail and then shifted outwardly when a wheel entered the retarder.

Bracket comprises an elongated L-shaped member mounted as by bolts 24 on adjacent cross ties in spaced parallel relation to rail 14, see FIG. 3. Bracket 27 is mounted in the same manner on the opposite side of rail 14 so that a description of bracket 25 applies to bracket 27 as well. Bolts 24 pass through apertures on the horizontal portion of bracket 25 and through holes drilled in the cross ties. Bracket 25 and lug 21 located on the right side of the rail, as oriented in FIG. 1, are positioned slightly farther from the rail 14 than bracket 27 and lug 23 located on the left side of the rail. This permits approximately centering the levers 17 and 19 and thus of is known, wheel 15 may run along the exact center of the rail.

A bed or tension plate 37 is affixed as by bolt 30 to one end of bracket 25 and extends parallel to the cross ties and the other end of bed plate 37 is aifixed as by bolt 32 to bracket 27. Likewise, a second bed plate 39 is similarly atfixed to the other ends of brackets 25 and 27. -Bed plates 37 and 39 provide a firm support for brackets 25 and 27 for opposing the forces which tend to separate the levers 17 and 19 and thus pivot pins '29 and 3 1 when the retarder is applying a braking force to a wheel. Thrust blocks 44 and 46 may be welded against the outside (with reference to the rail) of brackets 25 and 27 on bed plate 37 to firm the brackets in position and to reduce the stress on the various bolts.

The amount of force exerted by the brake shoes 11a and 13a on the wheel 15 is controlled by adjusting the.

spacing between pins 29 and 31 and also the spacing between each of the pins and the rail 14. As noted, it is desirable to have the brake shoes 1 1a and 13a provide a braking force at a relatively high point on the wheel 15; however, the force applied by the brake shoes to the wheel must not be so large as to squeeze out, i.e. push up and out, the wheels of light-weight cars. Shims 41 are utilized to adjust the position of lug 21. the desired distance from the rail 14 to thereby adjust the amount of force applied by shoes to the wheels; thus, the shims will compensate for shoe wear. Shims 41 are slotted to permit insertion orremoval withowthaving to remove the bolts 26. To move lug 21 toward the rail 14 and thus to position pivot pin 29 closer to the rail, bolts 26 are loosened, shims are removed from the right-hand side as oriented in FIGS. 1 and 2 of bracket '25 and im serted on the left-hand side of bracket 25 between the bracket and the lug 21. Similarly lug 23 and pivot pin 31 may be moved closer to the rail 14 by adjusting shims 42. v

A modification ot the retarder of FIG. 1 is shown in FIG. 4. Other than as described, the retarders of FIGS. 1 and 4 are similar and operate in a similar manner. A main diiference between the structure of FIG. 1 and that of FIG. 4 is that in FIG 4 the brackets 51 and 56 on which levers 17 and 19 are pivoted are mounted directly on the web 14b of the rail 14 as by bolts 55 which pass through apertures, not numbered, formed on the web of the rails. Also, the hubs '17a and 19a on levers 17 and 19 are formed to be somewhat larger, and the apertures, not numbered, in the hubs are formed to have diameters which are substantially larger than the diameter of the pivot pins 29 and 3-1. Eccentric bushings57 and 59' are circumposed about pins 29 and 31, and fitted into the apertures in the hubs 17a and 19a, respectively. Bushin-gs 57' and 59 each include portions extending out of hubs 17a and 19a such that a wrench of any suitable type can engage and turn bushings within their associated apertures. As shown in FIG. 4a the adjusting portion 57a of bushing 57 is positioned between a side of hub 17a1 and a side of extending portion 53a of bracket 53. A structural arrangement similar to this, although not shown, is provided for to facilitate the adjustment of bushing 59 in the hub 19a of lever 19. By turning the eccentric bushings, the distance lOf pins 29 and 31 and thus of levers .17 and 19, with respect to the rail 14,can be adjusted for purposes of controlling the force applied by the retarder on each car wheel as explained above- Set screws 611 and 63 lock the respective bushings 57 and 59 in their adjusted position.

A further difference between the structures of FIGS. 1 and 4 is that instead of brake'shoes 11a and 13a as shown in FIG. 1, track rails 65 and 67, somewhat m0dified in shape, mounted on levers 17 and 19 are utilized as brake beams as well as brake shoes for the retarders.

As is readily seen from FIG. 4, the rails 65 and 67 are wheel I mounted in a relatively horizontal plane'on the upper end of levers 17 and 19 as by bolts 20 and 16, respectively. What are normally the running surfaces 65a and 67a of rails 65 and 67 serves as the brake shoes. The lower portion, as oriented in FIG. 4, of each of the running surfaces 65a and 67a has been machined oif so that the surfaces 65a and 67a are effective to engage the side of the car wheel along a relatively narrow area at a relatively high point on the wheel; the purpose of so doing has been described above. The upper ends, as oriented in FIG. 4 of the bases of rails 65 and 67 have been cut ed to maintain car clearance.

A second modification of the retarder of FIG. 1 is shown in FIG. 5. FIG. is essentially similar to the structures of FIGS. 1 and 4 with the exception that FIG. 5 shows a different structure for positioning levers 17 and 19. In FIG. 5 the bracket 69 for aliixing the levers 17 and 19 in position comprises a flat portion or plate 69a which extends across the base 140 of the running rail 14. Bracket 69 is positioned between two adjacent cross ties. As can best be seen from FIG. 5a, bracket 69' includes upstanding lugs 69b and 69c, which lugs have apertures for receiving pivot pins 229 and 31, respectively. Clamps 79 positioned on each side of the base 14c of rail 14 are aifixed by means of bolts 71 to firmly clamp bracket 69 to the base 14c of rail 14. In FIG. 5a, some of the clamps '70 have not been included in order to more clearly show the structure of the plate 69a.

Referring now particularly to FIG. 3, the lengths of the brake beams, here numbered as 11 and 13, measured parallel to the running rail are limited to 11 feet. Since the minimum distance between axles of railway trains (even between coupled cars) is more than 11 feet this assures that only two wheels will be between the brake beams at a given time. If the brake beams are made longer than 11 feet, more than two wheels may be between the brake beams at one time, and since the thickness of car wheels commonly varies from 5 %1 to 5%, the two Wider wheels would hold the brake beams apart and the full braking action would not be efiective on all of the wheels.

Retarders can be positioned on only one or both running rails. If retarders are mounted on both rails, the spring centering action described above will tend to keep the wheels in line to remain on the track in the event one wheel climbs up and out of retarder while the wheel on the opposite side of the same axle remains down. Safe re-entrance of a wheel that has climbed out of the retarder back onto the running rail is still better assured if the retarders are positioned on only one rail and a guard rail 66 as shown in FIG. 3 is positioned adjacent the other rail opposite to the retarders. Reducing the track gauge as indicated above also tends to assure that any wheel that tends to climb out will re-en-ter or center back on its running rail.

Although the inert retarders were described above as primarily useful at exit of storage tracks in gravity type classification yards, it should be understood that they may also be used advantageously in other places such as in car dumper facilities and in industrial plant loading areas.

The efiectiveness of the inert retarder is necessarily less than that of power retarders since its braking force must be limited to that which will brake a light-weight car without squeezing out or causing the wheels of the light car to climb up and out of the retarder. Hence, utilizing five or six 11-foot retarders at the exit end of a classification yard track will not impose a serious load on the engine pulling out a string of cars, most of which cars are on a slight downgrade.

Wear rate of the retarder is relatively slow in sp1te of its being constantly biased to a braking position at all times.

Although we have herein shown and described only one form of apparatus embodying our invention, it is understood that various changes and modifications may be made 6 therein within the. scopeof the appendedc'laimswithout departing from the spirit and scope ofour invention. Having thus described our invention, what we claim is: 1. A railway car Wheel brake apparatus comprising a pair of brake beams positioned parallel to and straddling the rail for engaging the opposite sides of car wheels, pairs of vertically disposed levers, said brake beams being mounted on theupper end of said levers, each of said levers having an aperture intenmediate their ends, each of said apertures having inner and'outer surfaces, pins hav@ ing inner and outer surfaces passing through the apentures in each of said levers, said inner surfaces being nearestto the rail andsaid outer surfaces being farthest from the rail, a bushing ineach of said aperturesrotatablypositioned and eccentrically circurnposed on each of said pins, brackets for mounting said pins for pivoting said levers on said pins, Ibolt meansdfor adjusting the maximum spacing between the lower ends of said levers and thus the minimum, spacing between the upper ends of said levers for engaging the wheels, -a coil spring positioned between said levers and circumposed on said bolt means, said .bolt means being adjusted .to initially compress said spring, said spring effecting an initial force through said levers to said pins for centering said braking apparatus including said brake beams to an initial position for engaging the car wheels, said coil spring being additionally compressed when the'upper ends of said levers are forced apartas said brake beams engage a wheel to thereby provide a'braking force to the wheel, said initial force elfected by said spring and the force developed due to said braking force always providing a lateral loading on said inner surfaces of said pins whereby wear on said pins is reduced, and adjustable means rotatab-ly positionin said eccentric bushings about said pins to determine the spacing between said pins and said inner surfaces and thereby the spacing between said pins and wheels being braked whereby the braking force exerted by said spring on the 'wheels is controlled.

2. A railway car wheel brake apparatus comprising a .pair of brake beams positioned parallel to and straddling the running rail for engaging the opposite sides of car wheels, pairs of vertically disposed levers, each having an upper end, an intermediate portion and a lower end, said brake beams being mounted on the upper ends of said levers, each brake beam comprising a track rail mounted so that the running surface of the head of the rail provides the bnaking surface, said running surface of said head be ing formed to engage a relatively narrow area at a relatively high point on the sides of said wheels, each of said levers having an aperture intermediate its ends, each of said apertures having inner and outer surfaces, pins having inner and outer surfaces passing through the apertures in each of said levers for providing a pivot for said levers, said inner surface being nearest to the rail and said outer surfaces being farthest from the rail, a bushing eccentrically circumposed on the portions of each of said pins which pass through the apertures in each of said levers, a portion of said bushing projecting outside of the aperture in said levers and providing means for rotatably positioning said bushing on said pin, a bracket afiixed to the web of the rail. for mounting said pins, bolt and nut means at the lower ends of said levers for adjusting the spacing between the upper ends of said levers, a coil spring positioned between said levers and circumposed on said bolt means, said bolt means being adjusted to initially compress said spring, said spring effecting an initial force through said levers to said pins for centering said braking apparatus including said brake beams to an initial position for engaging the car wheels, said coil spring being additionally compressed when the upper ends of said levers are forced :apart as said brake beams engage a Wheel to thereby provide a braking force to the wheel, said initial force eife-cted by said spring and the force developed due to said braking force always providing a lateral loading on said inner surfaces of said pins whereby Wear on said pins is reduced, and said rotatable I '2 position of said eccentric bushings determining the spacing between said pins and said inner surfaces and thereby the spacing between said pins and wheels braked whereby the the rail for engaging the opposite sides of car wheels, pairs of vertically disposed levers each having an upper end, an intermediate portion and a lower end, said brake beams being mounted on the upper end of said levers, each of said levers having an aperture intermediate its ends, each of said apertures having inner and outer surfaces, pins having inner and outer surfaces passing through the apertures in each of said levers for providing a pivot for said levers, said inner surfaces being nearest to the rail and said outer surfaces being farthest from the rail, a bushing eccentrically circumposed on the portions of each of said pins which pass through the :aperatures in each of said levers, a portion of said bushing projecting outside of the aperture in said levers and providing means for rotatably positioning said bushing on said pin, mounting brackets having aperatured lugs for receiving said bushings and said pins, said brackets each comprising a plate extending beneath said rail and clampable on the base of the rail, bolt and nut means mounted through the lower ends of said levers for adjusting the maximum spacing between the lower ends of said levers and thus the minimum spacing between the upper ends of said levers for engaging the wheels, a coil spring positioned between the IOVIBI ends of said levers and eircumposed on said bolt means, said bolt means being adjusted to initially compress said spring, said spring eifecting an initial force through said levers to said pins for centering saidbraking apparatus including said brake beams to an initial position for engaging the car wheels, said coil spring being additionally compressed by said levers when said brake beams engagea wheel to thereby provide a braking force to the wheel, said initial 'forceetfected by said spring and the force developed due to said braking force always providing a lateral loading on said inner surfiaces of said pins whereby wear on said pins is reduced, and said rotatable position of said eccentric bushings determining the spacing between said pins and said inner surfaces and thereby the spacing between said pins and wheels being braked whereby the braking force exerted by said spring on the wheels is controlled.

References Cited in the file of this patent UNITED STATES PATENTS 9,916 Tuxworth Nov. 1, 1881 823,772 Fitch June 19 1906 1,852,572 Howe Apr. 5, 1932 2,116,174 Kay May 3, 1938 2,238,772 Clausen Apr. 15, 1941 2,285,327 Brown June 2, 1942 2,801,711 Field Aug. 6, 19.57 2,833,381 Frola May 6, 1958 2,913,071 Mueller Nov. 17, 1959' 2,947,385 Devaney Aug. 2, 1950 FOREIGN PATENTS Australia Dec. 22, 1949 

1. A RAILWAY CAR WHEEL BRAKE APPARATUS COMPRISING A PAIR OF BRAKE BEAMS POSITIONED PARALLEL TO AND STRADDLING THE RAIL FOR ENGAGING THE OPPOSITE SIDES OF CAR WHEELS, PAIRS OF VERTICALLY DISPOSED LEVERS, SAID BRAKE BEAMS BEING MOUNTED ON THE UPPER END OF SAID LEVERS, EACH OF SAID LEVERS HAVING AN APERTURE INTERMEDIATE THEIR ENDS, EACH OF SAID APERTURES HAVING INNER AND OUTER SURFACES, PINS HAVING INNER AND OUTER SURFACES PASSING THROUGH THE APERTURES IN EACH OF SAID LEVERS, SAID INNER SURFRACES BEING NEAREST TO THE RAIL AND OUTER SURFACES BEING FARTHEST FROM THE RAIL, A BUSHING IN EACH OF SAID APERTURES ROTATABLY POSITIONED AND ECCENTRICALLY CIRCUMPOSED ON EACH OF SAID PINS, BRACKETS FOR MOUNTING SAID PINS FOR PIVOTING SAID LEVERS ON SAID PINS, BOLT MEANS FOR ADJUSTING THE MAXIMUM SPACING BETWEEN THE LOWER ENDS OF SAID LEVERS AND THUS THE MINIMUM SPACING BETWEEN THE UPPER ENDS OF SAID LEVERS FOR ENGAGING THE WHEELS, A COIL SPRING POSITIONED BETWEEN SAID LEVERS AND CIRCUMPOSED ON SAID BOLT MEANS, SAID BOLT MEANS BEING ADJUSTED TO INITIALLY COMPRESS SAID SPRING SAID SPRING EFFECTING AN INITIAL FORCE THROUGH SAID LEVERS TO SAID PINS FOR CENTERING SAID BRAKING APPARATUS INCLUDING SAID BRAKE BEAMS TO AN INITIAL POSITION FOR ENGAGING THE CAR WHEELS, SAID COIL SPRING BEING ADDITIONALLY COMPRESSED WHEN THE UPPER ENDS OF SAID LEVERS ARE FORCED APART AS SAID BRAKE BEAMS ENGAGE A WHEEL TO THEREBY PROVIDE A BRAKING FORCE TO THE WHEEL, SAID INITIAL FORCE EFFECTED BY SAID SPRING AND THE FORCE DEVELOPED DUE TO SAID INNER SURFACES OF SAID PROVIDING A LATERAL LOADING ON SAID INNER SURFACES OF SAID PINS WHEREBY WEAR ON SAID PINS IS REDUCED, AND ADJUSTABLE MEANS ROTATABLY POSITIONING SAID ECCENTIRC BUSHINGS ABOUT SAID PINS TO DETERMINE THE SPACING BETWEEN SAID PINS AND SAID INNER SURFACES AND THEREBY THE SPACING BETWEEN SAID PINS AND WHEELS BEING BRAKED WHEREBY THE BRAKING FORCE EXERTED BY SAID SPRING ON THE WHEELS IS CONTROLLED. 